Many reactions among conventionally performed reactions are equilibrium reactions in each of which a forward reaction and a backward reaction exist at a certain constant rate. When the equilibrium of an equilibrium reaction is unfavorable for a product system side, at least one of products is generally separated from a reaction system to make the above-described equilibrium favorable for the product system favorable to increase reaction efficiency (equilibrium conversion rate). Various methods are known as a method of separating a product from a reaction system, and distillation separation is one of the most commonly performed methods. A method in which an equilibrium reaction is shifted to a product side to progress a reaction while removing a product from a reaction system by distillation is called reactive distillation, and for example, the explanation of reactive distillation is described in Non Patent Literature 1 by providing specific examples.
In general, reactive distillation is performed by using a distillation column such as a continuous multistage distillation column (reactive distillation equipment). When reactive distillation is performed in the distillation column, with the progress of a reaction, a higher-boiling component contained in a reaction liquid is distributed more in a lower stage side of the distillation column, whereas a lower-boiling component contained in the reaction liquid is distributed more in an upper stage side of the distillation column. Therefore, in the distillation column, the temperature in the column (liquid temperature) decreases from the bottom to the top of the column. The reaction rate of an equilibrium reaction decreases as the temperature becomes lower. For this reason, when reactive distillation is performed in the above-described distillation column, the reaction rate decreases from the bottom to the top of the column. More specifically, when reactive distillation is performed in the distillation column, the reaction efficiency of the equilibrium reaction decreases from the bottom to the top of the column.
In order to further improve the reaction efficiency, that is, to increase the reaction rate, a further increase in the temperature in the column has been studied. For example, Patent Literature 1 discloses a method of advantageously progressing a reaction by supplying a solvent to a reactive distillation column to raise the temperature in the reactive distillation column, as a method of efficiently performing an equilibrium reaction represented by Raw Material (P)+Raw Material (Q)Product (R)+Product (S), especially, an ester exchange reaction.
Moreover, use of a flow channel forming body called a micro channel reactor as reaction equipment for increasing the yield and the purity of a reaction product and safely performing a risky reaction is known (refer to Patent Literature 2). Since the micro channel reactor can efficiently transfer heat compared to an ordinary reaction container, a risky reaction such as nitration is perceived to be safely performed even at a high temperature. In addition, heating and cooling of a reaction system can be performed quickly, and the reaction can be easily controlled. Although the amount of a compound that can be handled with a micro channel reactor used in a laboratory is low, scale-up for industrial processes is possible by increasing the number of micro channels. Therefore, if the reactive distillation described above can be performed using a micro channel reactor, industrial value is high.
However, there is a problem in that a reaction in which some components become gases, such as reactive distillation, cannot be performed by a method using a micro channel reactor. This is because, in the continuous multistage distillation column (reactive distillation equipment) described above, a gas component is constantly extracted from a liquid phase, and thus, the concentration in the liquid phase becomes lower than the equilibrium value, and the equilibrium of an intended reaction can be shifted to a product side, but in the micro channel reactor, bubbles of generated gas are retained in a flow channel, and thus, the concentration of a gas component in a liquid phase achieves equilibrium due to the gas-liquid equilibrium of the gas component in the flow channel, and the equilibrium of a reaction to be performed is dominated by the concentration in the liquid phase.
With respect to this problem, for example, Patent Literature 3 discloses a method in which a reaction is performed while supplying gas to a flow channel to form a gas layer above a liquid phase in the flow channel, and making a by-product gas be trapped in the gas layer to be discharged out of the flow channel together with the gas layer. This method is intended to stabilize the liquid flow in the flow channel and shift the equilibrium of the reaction to a product side by making the by-product gas generated by the reaction be immediately trapped in the gas layer to be discharged out of the flow channel.